Thomas, expected to be the workhorse, is a rookie and was a true running back for only two years in college. Grigsby, too, is an undrafted rookie out of Arizona who has missed much of the last two seasons with injuries. Hilliard played special teams his first three years in Miami and has 23 career carries, all in 2009. Sheets, out for all of 2010 with a torn Achilles, has one career carry for five yards.

The old man in the group is Bush, who averaged a whopping 8.73 carries per game in his first five seasons. His career highs are 157 carries for 581 yards, and he’s never been the primary between-the-tackles running back.

“The lack of experience is definitely a concern,” Tony Sparano said Tuesday. “But I feel really good about the group that I have right now and I have really liked what I’ve seen out of them. You know, we have a little bit of everything back there.”

This group certainly possesses a lot of potential – Thomas led the Big 12 in rushing the past two years, while Bush provides a speed dynamic the Dolphins have lacked — and older vets like Brown and Williams certainly weren’t the answer last year.

But will Thomas’ skills translate to the NFL? Why are the coaches suddenly more comfortable giving Hilliard carries after keeping him off the field for three years? What if Bush or Thomas gets hurt? Can Grigsby or Sheets be quality backups?

The Dolphins sat idly as several veterans were scooped up by teams on the cheap over the past week – guys like Williams, Brown, Marion Barber, Cadillac Williams, Jason Snelling, Jerome Harrison, Jerious Norwood and Mike Bell. None of them would carry the Dolphins to the Super Bowl this season, but the Dolphins may regret not adding a veteran body to its inexperienced running back group.

2. Expect to see a good amount of Chad Henne vs. Falcons, but not other vets.

Sparano has a tricky decision to make with this Friday’s preseason opener against the Falcons.

On one hand, he doesn’t want to play the starters too much and risk injury in their first game action in seven months. On the other, the preseason games have added importance this August because of the loss of the offseason program, and players need the reps.

“I think as you get to the game, you got to identify, ‘Look I really don’t need to see this guy, but I need to see this guy this week a lot,'” Sparano said.

But expect to see a healthy amount of Henne, and perhaps receivers like Brandon Marshall and Brian Hartline. Though Henne’s a veteran with 27 career starts, he may need the live reps more than anyone on the team, given that he’s learning a new playbook and trying to build rapport with his receivers.

And the bottom-of-the-roster types probably won’t see too much game action.

“At some point here we really have to separate this team quickly and get to the guys that are going to play,” Sparano said.

3. Watch out for Roberto Wallace.

He came to the Dolphins last year as an undrafted rookie out of San Diego State with little experience – a native of Panama, Wallace was mostly a soccer player until trying his hand at football in 2004.

Wallace was mostly a bystander in 2010, catching just six passes for 62 yards all season. But Wallace, a physical specimen at 6-foot-4 and 225 pounds, has opened a lot of eyes this camp with his outstanding play on both offense and special teams.

“This guy has done a tremendous job in every special teams period that we’ve had out here,” Sparano said. “And then the second thing I’ve seen is that when the ball has been in the air in a competitive situation, kind of he versus the (defensive back), he has come down with it a few times in a crowd. He plays big, and that’s what you want a big receiver to do.”